1. Field of the Invention
The present invention relates to a fluid heating device, in more detail, a small-sized fluid heating device that can instantaneously heat fluid flowing for supply or circulation, due to high heating efficiency.
2. Description of the Related Art
A typical fluid heating device 1 is shown in FIG. 1, which is a storage-typed hot water supply system that heats a predetermined amount of water stored in a tank 2 and retains the heat always at predetermined temperature (e.g., about 40° C.)
Because the storage amount is limited in the storage-typed hot water supply system, hot water at predetermined temperature is supplied while the storage amount of water is discharged; however, the hot water gradually decreases in temperature and hot water under the predetermined temperature is discharged, when the system is used for a long time above the storage amount of water, such that it has a limit as a hot water supply system.
That is, it is limitative to use the system because the use time is limited and it is required to intermittently operate the system in order to supply hot water at predetermined temperature and keep the temperature.
Further, it is required to increase the size of the tank to ensure a predetermined storage amount and accordingly the system increases in size. It is also required to continuously supply electric power such that the temperature of the tank having predetermined heat loss is maintained in order to use the system at anytime. Therefore, the system unnecessarily wastes electric energy and causes a sanitary problem, because it keeps the temperature for bacteria and mold to easily proliferate.
An instantaneous-heating type fluid heating device 5 shown in FIG. 2 has been proposed, which uses a cylindrical ceramic heater in order to remove the defects of the storage-typed hot water supply system.
The fluid heating device 5 has the advantage of discharging hot water at predetermined temperature for a long time, because it can instantaneously heat the water (or fluid) flowing into a heating tank 7 through the cylindrical ceramic heater 6 at predetermined temperature, using electric heat from the ceramic heater 6.
However, it is difficult to accurately manufacture the cylindrical ceramic heater in order to reduce the diameter and the heating area is correspondingly reduced, such that it needs to maintain the size above a predetermined level. Meanwhile, when the heating area is large, the cross section of the flow path increases and the flow speed decreases, such that heat transfer efficiency is reduced and the thermal efficiency of the fluid heating device is correspondingly reduced.
In addition, it is limitative to reduce the size because of the dimension of the cylindrical ceramic heater and. Further, a predetermined amount of water is naturally stored, such that the control response becomes low and it is difficult to rapidly change the predetermined temperature.
In particular, the oxygen dissolved in the water cannot be instantaneously dissolved and a large amount of very small bubbles are generate due to the instantaneous heating. The bubbles can be discharged with the flow of water at high flow speed; however, the bubbles collect and remain on the surface of the ceramic heater and easily develop in a large bubble.
The large bubble developed from the bubbles collecting and remaining on the surface of the ceramic heater causes local thermal non-uniformity and a thermal shock in the ceramic heater, such that the ceramic heater is broken.
In order to prevent these problems, there has been effort of applying hydrophilic oxide on the surface of the ceramic heater such that to prevent the bubbles from developing on the surface. However, this method cannot be a basic solution, because various deposits are attached to the surface when it is used for a long period of time.
Further, the way of using the cylindrical ceramic heater has a fundamental problem in that the heating area is considerably reduced to increase the flow speed, whereas the flow speed on the ceramic surface is reduced to increase the heating area, due to a problem in the shape of the cylindrical ceramic heater.
FIG. 3 shows another fluid heating device 10 proposed in the related art, in which a ceramic flat plate heater 12 is interposed between flat plate device bodies 11 and flow paths 13 are formed in the device body 11 to form a heat transfer part.
According to the fluid heating device 10, although it is possible to achieve a small-sized device by implementing heat transfer through the flow paths formed in predetermined heating areas, the heating area is reduced by partitions 14 formed to forming the flow paths 13 and contacting the heating surface of the heater 12, such that the direct heating area contacting the fluid to heat is further reduced.
A dynamic heat transfer equilibrium state in which an inlet and an outlet of water is formed through a single ceramic heating surface may increase temperature difference in the ceramic plate heater, such that it is difficult to increase the size. However, when the size is reduced, it is required to increase the internal pressure for passing a predetermined amount of fluid due to the reduction of heat transfer area caused by forming the flow paths. Further, it is required to increase an output density per unit area.
Another similar configuration has been proposed, but, in which heat transfer is made while fluid flows through a plurality of flow paths arrange in parallel on one surface from the center of one flat plate ceramic heater and returns and flows through a plurality of flow paths formed on the opposite heating surface.
According to this configuration, fluid enters one side of the plate ceramic heater, flows to the opposite side through a plurality of flow paths formed on the heating surface, and then flows into a hot water sub-tank through a plurality of flow paths formed by copperplates on the opposite heating surface. In this structure, heat transfer is implemented through copperplates between the hot water sub-tank and the flow paths passing through the last heating surface entering hot water sub-tank.